This invention relates to a process for preparing a spherical green-emitting phosphor based on zinc orthosilicate and more particularly, to the process for a zinc orthosilicate-based green-emitting phosphor demonstrating an emission spectrum at visible regions, when excited by electron beam, via a new application of xe2x80x98the homogeneous precipitation methodxe2x80x99 comprising the following steps such as i) a solution of tetraethylorthosilicate (TEOS) diluted in ethanol is hydrolyzed to obtain a hydrated silica, ii) said hydrated silica is dispersed together with the solution containing zinc and manganese components, iii) a precipitant selected from oxalic acid and oxalates is added to said dispersed solution together with a basic solution, while precipitating zinc and manganese components, iv) said admixture precipitate, so filtered off and dried, is calcined in the air and reheated under the reducing atmosphere to prepare a phosphor powder; hence, the above-described phosphor powder particle is quite effective in a variety of display industrial fields including PDP use, since it has a spherical shape with less agglomeration and uniform distribution of manganese, an activator, thus proving superior to the conventional phosphor prepared by the solid state reaction method in terms of brightness.
Intensive researches have been focused on the green-emitting zinc orthosilicate-based phosphor used for the embodiment of various colors in the display industry. The typical Examples of such phosphor include a manganese-activated, green-emitting zinc orthosilicate phosphor having Zn2SiO4 as a matrix compound, while requiring Mn2+ ion as an activator so as to replace Zn2+.
Being known that the luminescent properties of phosphor are significantly dependent upon the particle size and the crystallinity, the exploitation for some novel matrix compounds, together with a novel synthetic method of phosphor , are under way in an effort to improve the luminescent properties of phosphor. The conventional method applied to prepare the zinc orthosilicate-based phosphor has been disclosed where the solid state reaction method conducted in a manner such that all starting solid materials are blended and heated for the manufacture of phosphor powder. According to the conventional method, however, the final calcination process should be performed at a very high temperature and this may result in the agglomeration of phosphor particles; if this is the case, the surface of phosphor may be damaged during the inevitably accompanied pulverizing process, or incorporation of impurities may function the formation of the dead layer on the surface of phosphor, thus resulting in the loss of emission intensity. For these reasons, other improved methods to replace the solid state reaction method are in urgent need. To comply with the above-described unfavorable situations, another solid state reaction technique was introduced using a flux to prepare the zinc orthosilicate-based phosphor, along with a co-precipitate process using sodium silicate or a sol-gel process. Nonetheless, these methods have failed to overcome the conventional drawbacks such as the non-uniform shape of phosphor particles and poor productivity. Meanwhile, to ensure a high-performance phosphor, it is a prerequisite that the size and the shape of phosphor particle and the homogeneous distribution of an activator in the parent lattice should be adjusted. With this in mind, there is an urgent need for the development of a novel synthetic process to prepare the zinc orthosilicate-based phosphor powder with uniform particles and good crystallinity.
Under such circumstances, the inventor et al. have conducted intensive studies to improve the luminescent properties of zinc orthosilicate-based phosphor through the synthesis of phosphor using a wet chemical process and noted that if the zinc orthosilicate-based phosphor is prepared via xe2x80x98the homogeneous precipitation methodxe2x80x99, a green-emitting phosphor with the improved emission intensity can be prepared to have fine particles of uniform spherical shape. Therefore, an object of this invention is to provide a novel synthetic process for preparing a zinc orthosilicate-based green-emitting phosphor with better luminescent property through the introduction of a novel xe2x80x98the homogeneous precipitation methodxe2x80x99, which has the following advantages compared with the conventional phosphor: (1) the particle size of phosphor powder is uniform and fine, (2) the phosphor powder has a spherical form with less agglomeration, and (3) the homogeneous distribution of an activator is ensured.